1. Field of the Invention
The present invention relates generally to a color display apparatus and, more particularly, to a color display apparatus using a one-panel diffractive-type optical modulator that is capable of forming diffractive light for incident light having a plurality of wavelengths using a single optical modulation device.
2. Description of the Related Art
With the development of micro technology, so-called micro Electro Mechanical Systems (MEMS) devices and small-sized equipment in which the MEMS devices are assembled have attracted significant attention.
A MEMS device is a device in which an actuation body which is formed on a substrate, such as a silicon substrate or a glass substrate, in a micro-structure form and configured to output mechanical actuation force, and a semiconductor Integrated Circuit (IC) that is configured to control the actuation body are electrically and mechanically combined. The MEMS device is basically characterized in that the actuation body having a mechanical structure is a part of the device, and the operation of the actuation body is electrically performed using Coulomb's force between electrodes.
FIG. 1 is a view showing the construction of a Grating Light Valve (GLV) device that Silicon Light Machine (SLM) Inc. has developed as a light intensity conversion device for a laser display, that is, an optical modulator.
The GLV device 21, as shown in FIG. 1, is configured such that a common substrate-side electrode 23 is formed on an insulation substrate 22, such as a glass substrate, a plurality of beams 24, for example, six beams 241, 242, 243, 244, 245 and 246 in the present invention, that cross the common substrate-side electrode 23, are installed in a bridge form, and are arranged in parallel.
The beams 24, each of which is formed of a bridge member 25 and a combined reflective layer and actuation-side electrode 26 mounted on the bridge member 25, are parts that are collectively called ribbons.
When minute voltage is applied between the substrate-side electrode 23 and the combined reflective layer and actuation-side electrodes 26, the beams 24 approach the substrate-side electrode 23 due to the above-described electrostatic phenomenon. In contrast, when the application of voltage is stopped, the beams 24 move away from the substrate-side electrode 23 and are restored to their original positions.
The GLV device 21 alternately varies the heights of the combined reflective layer and actuation-side electrodes 26 due to the approach and separation operation of the plurality of beams 24 with respect to the substrate-side electrode 23 (that is, the approach and separation operation of alternate beams), and modulates the intensity of light reflected from the actuation-side electrode 26 using the diffraction of light (one light spot is irradiated for all of the six beams 24).
FIG. 2A is a diagram showing an example of a conventional one-panel optical apparatus using a GLV device as an optical modulation device to which a MEMS device is applied, or using a piezoelectric diffractive-type optical modulator.
Referring to FIG. 2A, the conventional one-panel optical apparatus includes a light source system 50, a light condensing unit 52, an illumination lens system 54, a flat-type color wheel 57, a GLV device 58, a Fourier filter system 59, a projection system 62, and a screen 65.
The light source system 51 is formed of a plurality of light sources 51a to 51c, and the light-condensing unit 52 is formed of a single reflective mirror 53a and a plurality of dichroic mirrors 53b and 53c. 
The plurality of light sources 51a to 51c includes, for example, a Red (R) light source 51a, a Green (G) light source 51b, and a Blue (B) light source 51c. The light condensing unit 52 condenses a blue-colored light, a green-colored light and a red-colored light using the single reflective mirror 53a and a plurality of dichroic mirrors, so that a multi-beam is formed, therefore a single illumination system is constructed.
Subsequently, the illumination lens system 54 converts the condensed multi-beam into a linear parallel light beam, and causes the linear parallel light to enter into the GLV device 58 through the flat-type color wheel 57.
In more detail, the flat-type color wheel 57 includes color filters that allow only light beams of the multi-beam corresponding to respective colors to pass therethrough, a coupler to which the color filters are attached, and a motor that is attached to the coupler and configured to generate rotational force. The flat-type color wheel 57 sequentially separates the colors of light beam from each other as the coupler and the color filters attached to the coupler in a flat form rotate according to the rotational velocity of the motor.
When a linear parallel light having a single wavelength enters from the flat-type color wheel 57, the GLV device 58 forms diffractive light by performing optical modulation on the linear parallel light having the corresponding wavelength for the entering time, and causes the formed diffractive light to be incident on the Fourier filter system 59.
It is preferred that the Fourier filter system 59 be composed of a Fourier lens 60 and a dichroic filter 61. The Fourier filter system 59 separates the diffractive light according to order and passes only desired orders of diffractive light therethrough.
Meanwhile, the projection system 62 includes a scanner 63 and a projection lens 64, and projects the entering diffractive light onto the screen 65.
FIG. 2B is a diagram showing an example of a conventional three-panel optical apparatus using a GLV device as an optical modulation device to which a MEMS device is applied, or using a piezoelectric diffractive-type optical modulator. In the present example, a case where the optical apparatus is applied to a laser display is described
The laser display 51 related to the present example is used as, for example, a large-sized screen projector and, in particular, a digital image projector or the image projection apparatus of a computer.
The laser display 51, as shown in FIG. 2B, include laser light sources 52R, 52G and 52B, respectively provided with R, G and B colors, mirrors 54R, 54G and 54B respectively installed on the optical axes of the laser light sources, color illumination optical systems (lens group) 56R, 56G and 56B, and GVL devices 58R, 58G and 58B.
The laser light sources 52R, 52G and 52B, for example, emit an R laser beam (having a wavelength of 642 nm and an optical output of about 3 W), a G laser beam (having a wavelength of 532 nm and an optical output of about 2 W), and a B laser beam (having a wavelength of 457 nm and an optical output of about 1.5 W), respectively.
Furthermore, the laser display 51 includes a color synthesizing filter 60 for synthesizing the R, G and B laser beams whose intensities of light are respectively modulated by the GVL devices 58R, 58G and 58B, a spatial filter 62, a diffuser 64, a mirror 66, a Galvano-scanner 68, a projection optical system (lens group) 70, and a screen 72. The color synthesizing filter 60 includes, for example, a dichroic mirror.
In the laser display 51 of the present example, RGB laser beams emitted from the laser light sources 52R, 52G and 52B respectively pass through the mirrors 54R, 54G and 54B, and are respectively incident on the GVL devices 58R, 58G and 58B of the color illumination optical systems 56R, 56G and 56B. The laser beams are color-separated video signals, and are input to the GVL devices 58R, 58G and 58B in a synchronized manner.
Furthermore, the respective laser beams are diffracted by the GVL devices 58R, 58G and 58B, thus being spatially modulated. These tri-color diffractive light beams are synthesized by the color synthesizing filter 60 and then only signal components are extracted by the spatial filter 62.
Thereafter, the RGB video signals experience a decrease in the laser spectrum thereof by the diffuser 64, are emitted on a space by the Galvano-scanner 68 that is synchronized with video signals through the mirror 66, and are projected in full-color image form onto the screen 72 by the projection optical system 70.
Meanwhile, as described above, the one-panel-type optical apparatus has a simple structure, reduces cost, and enables the realization of the optical system. However, the one-panel-type optical apparatus is problematic in that the optical modulator used requires operation velocity three times faster than that of an existing modulator and, therefore, the life span thereof is reduced by ⅓. Furthermore, the one-panel-type optical apparatus is problematic in that light efficiency is lowered because a color wheel is necessary.
Furthermore, the three-panel-type optical apparatus is problematic in that the optical systems thereof are complicated and the cost thereof increases because optical modulators are provided so as to correspond to respective colors of laser light sources.